Double-acting hydraulic cylinders are now widely used in exercising apparatuses to provide a resistance to a user who is exerting a force on the cylinder thereby to strengthen his (her) muscles.
However, the conventional double-acting hydraulic cylinder used in an exercising apparatus has the following disadvantages.
Firstly, when a piston of the hydraulic cylinder is forced to move within the hydraulic cylinder from one side to another side, the side of the hydraulic cylinder from which the piston is moved away cannot be immediately supplied with hydraulic oil in the hydraulic cylinder; thus, when a user exerts a pulling force immediately following exerting a pushing force on the hydraulic cylinder, at the beginning of the pulling operation, he (she) will experience a period of operation in which there is substantially no resistance from the hydraulic cylinder, which causes the operation of the apparatus to be not smooth.
Secondly, since the resistance obtainable from the conventional hydraulic cylinder is constant, the versatility of the conventional hydraulic cylinder is limited. The resistance of the conventional hydraulic cylinder cannot be adjusted to meet the different requirements of different users; for example, an adult may require a heavy resistance and a youth may require a light resistance from the hydraulic cylinder.
The present invention therefore is aimed to provide an improved double-acting hydraulic cylinder used in an exercising apparatus to mitigate and/or obviate the aforementioned problems.